Conventional multitransducer recording heads for bidirectional linear tape drives have transducers fabricated on a ferrite or other ceramic substrate using thin film wafer technology. Bleed slots for removing air are cut into the ferrite substrate transducing surface on both sides of the transducers, and the surface is then lapped to a desired contour. The conventional contour comprises a cylindrical or complex shape which is critical in maintaining the moving tape at the desired head to transducer spacing (called "contact" recording). The contact, or near contact, spacing is maintained by controlling the contour shape to "bleed", "skive" or "scrape" the boundary layer of air carried by the tape away and into the bleed slots before encountering the transducer to prevent the tape from "flying", or losing contact with the transducer.
The contact between the magnetic head and the magnetic tape is crucial so that the recording gaps of the transducers, which are the source of the magnetic recording flux, are in intimate or near contact with the tape to effect efficient signal transfer, and so that the playback element is in intimate or near contact with the tape to provide effective coupling of the magnetic field from the tape to the playback element.
Typically, the contour is designed with a small radius and a high wrap angle so that high pressure is exerted on the head while the tension is low. However, the contour of the head must be such that the pressure of the tape on the transducer is not so high that the surface of the transducer wears excessively.
Such heads are often provided with "outriggers" on both sides of the head which help support the tape and reduce head wear, but, more importantly, control the wrap angle of the tape with respect to the head. Any change in radius will change the pressure of the tape on the head at the same tape tension.
Referring to FIGS. 1 and 2, prior art bidirectional linear tape drives have typically used tape heads with a cylindrical contour.
The prior art high speed bidirectional linear tape head of FIG. 1 illustrates two modules 10 and 11, each having a transducing gap 12, with cross slots 14 to bleed out air entrained between the head contour and moving tape. The conventional cylindrical contour 15 is used to maintain the moving tape in contact or near contact with the head. The contact, or near contact, spacing is maintained by controlling the contour shape to bleed the boundary layer of air carried by the tape away and into the bleed slots 14 before encountering the transducer to prevent the tape from "flying", or losing contact with the transducer.
The prior art low cost bidirectional tape head of FIG. 2 employs a single module 16 of two halves forming a single transducing gap 17 employing a small radius cylindrical contour 18 with a very short land of about 14 degrees and an edge 19 to remove the entrained air without the need for air bleed slots. Lapping of the tape head assembly and of the corresponding outriggers to a contour is very expensive and is a major contributor to the manufacturing cost of the tape head.
A 1973 patent, U.S. Pat. No. 3,737,582 suggests a substantially flat ferrite magnetic core head with carbide inserts at the edges. The edges are required to have a back angle of 95 degrees from the tape direction to provide self-sharpening of the edges. Unlike modern thin film heads, intimate contact with the transducing gap was not required. With modern thin tapes and high tape speeds, the head and the tape must be in intimate contact and this will cause undesirable wear to the ferrite and in the gap area between the inserts. This means that upon a change in tape thickness or tension that intimate contact with the tape would be lost.
A flat contour linear tape head has been proposed for a single direction magnetic tape drive, which must rewind the tape out of contact with the head upon the completion of reading and/or writing the tape. "Contact Tape Recording with a Flat Head Contour", H. Hinteregger and S. Muftu, Massachusetts Institute of Technology Haystack Observatory, Westford, Mass. 01886, Mar. 2, 1996. The flat contour head comprised a row of thin film disk heads formed on ceramic, and the tape was wrapped at approximately 2 degrees over the hard ceramic corner of the bar and not wrapped at all over the soft thin film trailing corner.
The flat contour also provided good transducing and wear characteristics, but was not usable in a bidirectional linear tape drive.